Activation key for parallels 5 doesn't work in snow leopard

I bought the upgrade version of par. 5 for snow leopard. Activation key on back of envelope does not work. I also own par. 3 for MAC OS tiger, I tried that key too. I did not install old version in snow leopard, since I read it is not compatible. I finally got a trial ver. activation key, but how do I get my "real" paid for key to work without paying $20 for tech support??